Vent-run gas switching systems are commonly used in the growth of multi-layer thin films. Two common example applications are the manufacture of Al2O3 and TiN films. In such applications, sources of two or more gaseous species to be deposited are provided. A purge gas source may also be provided. The gases are delivered to a process chamber, sequentially, by means of a switching system between the gas sources and the process chamber. Any residual species, purge gas or by-products are exhausted from the process chamber by a pump.
Typically, purge gas is passed through the reaction chamber between supplies of the species to be deposited. The purpose of the purge gas is to remove any residual (not deposited) species from the process chamber so as to prevent reaction with the next species supplied to the chamber. Were the species allowed to cross react, this might result in impurities and imperfections in the multi-layer film.
In existing vent-run gas switching systems, gases leaving the process chamber enter a common foreline leading to a vacuum pump. Cross reaction of any residual species can occur in the foreline and this can result in the accumulation of particulates in the foreline leading to impaired pump performance. Such impairment of pump performance may compromise the quality of the product manufactured in the process chamber. In addition, the process down time involved in repairing and maintaining affected pumps can increase the costs of manufacture.
The present invention aims to provide apparatus wherein cross reaction of species on exhaust from the process chamber is significantly reduced.